This invention relates to apparatus for punching holes in sheet metal and the like and, more particularly, to novel and highly effective hole punch apparatus that is unusually compact, light, easy to use, and inexpensive.
Electricians and others must frequently punch holes of fairly large diameter in sheet metal and the like in order to pass cable, etc. Large holes cannot conveniently be drilled in sheet metal, and the usual practice is first to drill a small hole and then to use a punch and die (hereinafter sometimes referred to collectively as "dies") to punch a hole of the required size. The punch and die are placed on opposite sides of the workpiece so that they are concentric with the drilled hole. A shaft is passed through an aperture in the die and through the drilled hole and engaged with the punch. Then by means of a hydraulic system or a system comprising hand operated levers the punch and die are drawn forcibly together, compressing the workpiece between them and cutting the hole of required size.
A good hydraulic system works very well but is expensive. Systems comprising hand operated levers work less well and require considerable effort to operate. Moreover, two handles are necessary, one normally being ratcheted to permit operation in a confined space and the other being provided merely for the purpose of offsetting the considerable torque that would otherwise be transmitted to the workpiece.
Both hydraulic systems and systems employing hand operated levers are bulky and heavy. Since these tools must generally be carried from one job to another, their bulk and weight constitute a serious drawback.